Method and device for the investigation of substances by slowly moving neutrons



June 17, 1941.

H. l. KALLMANN, FORMERLY KNOWN AS HARTMUT KALLMANN ETAL METHOD AND DEVICE FOR THE INVESTIGATION OF SUBSTANCES BY SLOWLY MOVING NEUTRONS File d Jan. 20, 1939 Patented June 17, 1941 UNITED STATES PATENT OFFICE METHOD AND DEVICE FOR THE INVESTIGA- TION OF SUBSTANCES BY SLOWLY MOV- ING NEUTRON S Application January 20, 1939, Serial No. 252,049 In Germany January 24, 1938 3 Claims. $(Cl. 250-65) :This invention relates to the art of investigating substances with the aid of neutrons, and is particularly concerned with the provision of a device adapted for showing the distribution of the intensity over a beam of slowly moving neutrons.

It has already been suggested to investigate substances which absorb or scatter neutrons by means of slowly moving neutrons. This method is carried out in the manner that the substance to be investigated is traversed by slowly moving neutrons and the neutrons leaving the traversed substance are made to impinge upon an intermediate layer in which takes place a reaction producing heavy charged particles which latter affect a directly adjacent photographic system (as described and claimed in our copending application Serial No. 197,929), now Patent No. 2,- 186,929. The heavy particles can also be caused to excite a fluorescent screen located directly adjacent to said intermediate layer whereby they produce an image of the distribution of the intensity over the neutron-beam on the fluorescent screen (as disclosed and claimed in our copending application Serial No. 197,928), now Patent No. 2,188,115. When producing a photographic image of a neutron-beam the intermediate layer is formed by a foil of lithium or boron or of a composition containing one or both of .these materials. If a fluorescent screen is used the screen is likewise provided with such an intermediate layer or the fluorescent substance is mixed with a composition containing boron or lithium.

For the objective fixing or the image excited by a neutron-beam on a fluorescent screen it is advantageous to combine the J'ustmentioned two methods. According to this invention, a photographic layer is therefore brought into the neighborhood of, or into direct contact with, a fluorescent substance, said fluorescent substan-ce being applied to a layer consisting of a composition containing lithiumpr boron, or mixed with any of these substances or a composition containing any of them.

In any of these cases the particles produced by the action of the unabsorbed slowly moving neutrons upon the lithium or boron will act first of all upon the fluorescent substance, and the radiation excited in the latter will then blacken the said photographic layer. Simultaneously therewith, the heavy particles can also directly blacken the photographic layer.

It is also advantageous, under some circumstances, to arrange the fluorescent substance, provided with a lithium (or boron) layer together with the photographic layer, in an air-tight container which is either evacuated or filled with an indifferent gas.

energize the adjacent layer 4 of fluorescent sub- A plurality of such plates or films may be arranged behind one another; and in the neighborhood of each of the photographic layers one or two fluorescent screens of the above described kind may be provided.

In order to protect the photographic layer from any chemical influence oi the lithium-containing layer, especially if the percentage of lithium therein is large, a special protective layer may be provided which is permeable by the rays emitted by the fluorescent screen.

The invention is now more specifically described with reference to the accompanying drawing in which the single figure schematically illustrates the device of the present invention and a mode of using the same.

In the figure, a source of neutrons is conventionally indicated at I. 2 is the body being investigated. The device of the present invention is the combination 3, 4, 5, in which 3 repre sents an intermediate reaction layer containing lithium and/or boron, 4 represents a layer of fluorescent substance, and 5 represents a photographic layer.

In use, neutrons proceeding as a beam from source of neutrons I impinge on the body 2 to be studied and are in part absorbed in the latter. Unabsorbed neutrons impinge upon the lithium (or boron) layer 3. Heavy particles dissolved from the nuclei of the lithium (or boron) stance. Radiation excited by the energized layer 4 acts on the adjacent photographic layer 5, whereby an objective fixing of the image excited by .the neutron beam is effected.

We claim:

'1. A device for forming a photographic image of the distribution of the intensity over a beam of slowly moving neutrons, which comprises the combination of a photographic layer and a fluorescent screen associated with a composition containing a neutron-reactive element of the group consisting of lithium and boron, the fluorescent screen being arranged in the neighborhood of said photographic layer in such a way that rays emitted by the said screen act upon said photo graphic layer.

2. The device defined in claim 1, in which the composition containing the neutron-reactive element is contained in the fluorescent screen.

3. The device defined in claim 1, in which the composition containing the neutron-reactive element is extended in the form of a layer adjacent that side of the fluorescent screen which is remote from the photographic layer.

HARTMUT ISRAEL KALLMANN, Formerly known as Hartmut Kallmann.

ERNST Kill-IN. 

